The goal of the proposed project is to elucidate the roles, mechanisms and features of a recently discovered immune suppressive T cell subset, T regulatory (Treg) cells, in the context of periodontal pathogenic adaptive immune responses (PPAIR). Treg cells are distinct from T effector cells (Th1-, Th2- or Th17-cells) based on their profiles of cytokine production (IL-10 and TGF-2) as well as their expressions of a unique transcription factor, FOXP3, and concomitantly expressed CD25. Importantly, Treg cells are known to suppress adaptive immune responses occurring in autoimmune and infectious diseases and in many other immune-response related outcomes. Thus, upon successful characterization of Treg's molecular-immunological mechanisms, via our mouse model of periodontal disease (PD), we will have gained the understanding required for future human clinical trials. This translational strategy should lead to the development of novel drug-free and side- effect-free therapeutic approaches to the treatment human periodontal bone loss and tissue destruction, as well as other immune-associated oral diseases. One such approach, UV illumination, is summarized below. The pathogenic involvement of adaptive immune response was demonstrated by our recent discovery that the osteoclast differentiation factor, RANKL, is distinctively expressed by activated T cells and B cells in gingival tissues with periodontal disease, but not by these cells in healthy gingival tissues. We recently found that the prevalence of FOXP3 expression by CD25+ T cells, which do not express RANKL, was significantly lower in human gingival tissues with periodontal disease than in healthy tissues. Based on a mouse model of periodontal disease, our preliminary studies indicated that adoptive transfer of CD25+ Treg cells, which were ex vivo-expanded with Treg developing factor, TGF-2, could ameliorate the periodontal bone loss induced by PPAIR induction, as well as inhibit in vitro antigen-specific proliferation of Th1 effector cells and their production of RANKL. These conclusions have, in turn, led us to speculate that UV illumination in general, and UVB illumination in particular, could have a novel therapeutic use in the treatment of periodontal disease. That is, since UVB is used to augment the Treg cell population in the treatment of psoriasis, a skin disease hypothesized to be immune-mediated, then the same technique should up-regulate TGF-2 expression in mouse gingival epithelium, resulting in an increase of FOXP3+/CD25+ Treg cells in the gingivae. Such a previously optimized research platform will permit us to elucidate the as yet unstudied roles, features and mechanisms of Treg cells in the context of periodontal disease. Therefore, in the proposed project, we will investigate 1) the requirement of antigen specificity by Treg cells in their suppression function to PPAIR-induced bone resorption, 2) the roles and mechanisms of Treg cells on the regulation of PPAIR- induced periodontal bone resorption;and 3) the development of a promising phototherapeutic approach to PD, which utilizes the phenomenon of Treg induction by gingival UV illumination. PROJECT NARRATIVE: Our studies will generate empirical data confirming the prevalence and activity of a recently discovered immune suppressive lymphocyte subpopulation, T regulatory cells (Treg). To date, the immune suppressive function of Treg has only been sparsely studied, and its roles, mechanisms, and features, in terms of periodontal pathogenic adaptive immune response (PPAIR), have not been studied at all. Therefore, the proposed project will employ both a mouse model of periodontal disease, as well as periodontally diseased human gingival tissues, to illuminate our understanding of the commonalities between mouse and Treg-mediated immune intervention in the pathogenesis of PD. To the extent that these results are translational, we can begin to develop novel therapies. One such promising therapeutic modality is the application of phototherapy, in the form of UVB illumination, to the lesions of diseased tissue. This is the key therapeutic strategy that forms the foundation of our study. Augmentation of Treg-activity is implicated in the treatment of psoriasis by UVB illumination. Thus, we believe that the trials we plan for our mouse in vivo model will prove equally effective in inducing human in vivo Treg and thereby possibly ameliorating the bone destructive effects of PPAIR.